Fix the problem with updating the reply_to or service_letter_contact_id for templates.

The history was not being updated properly, we think this is because the declaritive attribute is not being set propery by the property.
When reply_to: None it will update the service_letter_contact_id, but not the service_letter_contact, we think when the history_meta is build the history class and checking if the value is updated it depends which attribute it is checking first.

In order to fix this issue, there is a new dao method to update the reply_to on the Template and insert a new Template history.

tests/app/template/test_rest.py

@@ -662,6 +662,28 @@ def test_update_template_reply_to(client, sample_letter_template):
     assert th.service_letter_contact_id == letter_contact.id
 
 
+def test_update_template_reply_to_set_to_blank(client, notify_db_session):
+    auth_header = create_authorization_header()
+    service = create_service(service_permissions=['letter'])
+    letter_contact = create_letter_contact(service, "Edinburgh, ED1 1AA")
+    template = create_template(service=service, template_type='letter', reply_to=letter_contact.id)
+
+    data = {
+        'reply_to': None,
+    }
+
+    resp = client.post('/service/{}/template/{}'.format(template.service_id, template.id),
+                       data=json.dumps(data),
+                       headers=[('Content-Type', 'application/json'), auth_header])
+
+    assert resp.status_code == 200, resp.get_data(as_text=True)
+
+    template = dao_get_template_by_id(template.id)
+    assert template.service_letter_contact_id is None
+    th = TemplateHistory.query.filter_by(id=template.id, version=2).one()
+    assert th.service_letter_contact_id is None
+
+
 def test_update_template_with_foreign_service_reply_to(client, sample_letter_template):
     auth_header = create_authorization_header()